Gas sensor

ABSTRACT

A gas sensor is disclosed which attains high response speed, low power consumption, superior water splash resistance and a little setting direction dependency and setting angle dependency. In this gas sensor, a measured gas room is provided inside an inner cover, and gas passage holes for leading a measured gas in are provided on side surfaces of the inner cover and an outer cover. The gas passage holes provided on the outer cover are positioned much closer to a top end side than the gas passage hole provided closest to the top end side in the inner cover. Partitions disposed extendedly in an axial direction of the gas sensor are provided between the outer cover and the inner cover.

This application is a division of application Ser. No. 10/175,090, filedJun. 20, 2002, now U.S. Pat. No. 6,780,298, the entire contents which ishereby incorporated by reference in this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a gas sensor placed in an exhaustsystem of an internal combustion engine and used for combustion control.

2. Description of the Prior Art

Gas sensors installed in an exhaust system of an internal combustionengine such as an automobile engine and used for combustion controlinclude an O₂ sensor, an air fuel ratio sensor, an NOx sensor, an HCsensor and the like. Elements built in these gas sensors include acup-shaped gas sensor element comprising a cup-shaped solid electrolyte,and a laminated gas sensor element constituted by laminating ceramicsheets, electrodes and the like owing to limitations such as earlyactivation or detection principles (e.g., Japanese Patent ApplicationPublication No. H9-127050).

The gas sensor element provided in the gas sensor must be exposed to anexhaust gas for gas density measurement, while the gas sensor elementmust be protected against characteristic deterioration caused by poisonof the exhaust gas or against an element crack caused by water splash.For such reasons, a cover is provided for covering the gas sensorelement. The cover has gas passage holes on its side surface or the liketo lead the exhaust gas into a measured gas room formed inside thecover.

Incidentally, it has conventionally been known that the constitution ofthe cover is contrived so that the flow velocity of the exhaust gas maynot have an influence on an output of the gas sensor when the exhaustgas is led into the cover from the gas passage hole (Japanese UtilityModel Publication (after examination) No. H3-4930).

Furthermore, it has been known that the constitution is contrived sothat it may be difficult for water spattering through an exhaust pipe inwhich the gas sensor is provided to get inside the cover from the gaspassage hole (Japanese Patent No. 2641346, Japanese Patent ApplicationPublication No. H9-222416).

Still further, when the element is the laminated one, in some cases, adifference arises in a positional relation between a gas flow directionand a normal direction of the gas sensor element at the time of settingthe gas sensor. In this case, the cover contrived to reduce thedifference of response speeds (directionality) caused by setting stateis also known (Japanese Patent No. 2653831). However, the covers ofconventional constitutions present a problem of slowed response speed ifthe directionality or water coming in is reduced.

Further yet, another problem is that the difference of the responsespeeds (setting angle dependency) is large when the positional relationbetween an axial direction of the gas sensor element and the gas flowdirection is different. For example, in Japanese Patent No. 2653831mentioned above, the gas passage holes are disposed closer to a tip endside than a gas leading part of the gas sensor, so that a gas componentdesired to be detected needs to reach the measured gas room by usingonly turbulence diffusion. Therefore, the response speed is slowed downcompared to the case of the cover having the constitution that leads thegas in by using a steady flow.

Further yet, in Japanese Utility Model Publication (after examination)No. H3-4930 mentioned above, because the flow of the measured gas insidean inner cover is not uniform, the directionality occurs in the responsespeed, causing the difference of the response speeds to be 10 ms ormore. This makes a large difference of the characteristics dependingupon the setting directions of the gas sensor, which might make itimpossible to expect accurate gas density measurements. In JapanesePatent No. 2641346 mentioned above, because the gas passage hole is notprovided in a bottom surface part of the inner cover, the amount of gasflowing into the inner cover is small, and the response speed istherefore slowed down. Further, as the flow in the inner cover is notuniform, the directionality emerges. Further, if the area of the gaspassage hole is enlarged to increase the response speed, the elementcrack due to the water splash is more likely to occur, and moreover,when the element is heated by a heater to keep a constant temperature,there is a problem of increased power consumption.

Incidentally, in German Patent No. 19628423A1, the side surface of anouter cover does not have the gas passage holes, and it is designed tolead the gas that will flow into the inner cover from the gas passagehole provided on the bottom surface of the outer cover. However, becausethis gas passage hole is vertical to the gas flow, it has resistance tothe gas inflow and poses a problem of the slowed response speed.Further, if a tip end portion of the element is set inclining to adownstream side of the exhaust gas flow, it raises a problem of theslowed response speed, and if it is set inclining to an upstream side,it raises a problem of deteriorated water splash resistance.

In both of German Patent No. 19628423A1 and German Patent No. 4436580A1,because the inner cover projects from the outer cover, the inner coveris exposed directly to the gas flow, and therefore the inner cover iscooled down. Since a radiant heat quantity from the gas sensor elementis proportionate to the fourth power of the temperature of the innercover, the power consumption increases when the inner cover is cooleddown.

In Japanese Patent Application Publication No. H9-222416, since thebottom surface of the inner cover and the bottom surface of the outercover are kept away, the exhaust gas that has got in from the gaspassage hole on the side surface of the outer cover flows out from thegas passage hole on the bottom surface of the outer cover. This reducesthe amount of gas flowing into the inner cover, and the response speedis thus slowed down.

In Japanese Patent Application Publication No. 2000-171429, if the tipend portion of the element is set inclining to the downstream side orthe upstream side toward the flow of the exhaust gas, it raises aproblem that responsiveness is slowed down. In other words, the settingangle dependency is increased, giving trouble in setting operation ofthe gas sensor.

SUMMARY OF THE INVENTION

The present invention has been made in view of such conventionalproblems, and is intended to provide a gas sensor with a high responsespeed, low power consumption, superior water splash resistance and alittle setting direction dependency and setting angle dependency.

One aspect of the present invention is in a gas sensor comprising a gassensor element and a cylindrical housing for inserting and fixing saidgas sensor element, measured gas side covers having a bottom andprovided on a tip end side of said housing and an atmosphere side coverprovided on a base end side, wherein

said measured gas side covers comprises an inner cover for directlycovering the gas sensor element and an outer cover directly exposed tomeasured gas ambience, and are provided with a measured gas room insidesaid inner cover;

gas passage holes for leading a measured gas into said measured gas roomare provided on side surfaces of said inner cover and said outer coverrespectively, and the gas passage hole provided on said outer cover isdisposed in a position much closer to the tip end side than the gaspassage hole provided closest to the tip end side in said inner cover;and

partitions disposed extendedly in an axial direction of the gas sensorare provided between said outer cover and said inner cover.

Next, functional effects of the present invention will be described. Inthe gas sensor in accordance with the present invention, the partitionsdisposed extendedly in an axial direction are provided between the outercover and the inner cover, and consequently, it is possible to preventthe measured gas that has got in from the gas passage hole on the outercover from passing other gas passage holes to flow out of the outercover again, and further possible to rectify a gas flow between theouter cover and the inner cover so that the measured gas can quicklyreach the gas passage hole on the inner cover along the partitions. Inthis way, since the measured gas can quickly reach the measured gas roominside the inner cover, it is possible to make the response speed of thegas sensor faster.

Furthermore, since the partitions function as guide plates of themeasured gas, the measured gas can be led from the gas passage holes tothe measured gas room always in the same state, without depending uponthe setting direction and setting angle of the gas sensor.

Still further, the gas passage hole provided on the outer cover isdisposed in a position much closer to the tip end side than the gaspassage hole provided closest to the tip end side in the inner cover.This makes it possible to prevent the gas passage holes on the outercover and those on the inner cover from being in a confronting state,and thus both the flow holes will be in a communicating state, therebypreventing water drops from getting in from the outside. This means thatwhen the water drops get in from the gas passage hole of the outercover, it is difficult for the water drops to reach the gas sensorelement in the measured gas room by the blocking of the inner cover. Inthis way, the gas sensor in accordance with the present invention hashigh water splash resistance.

Further yet, as it is not necessary to enlarge the diameter of the gaspassage holes to enhance responsiveness, the inflow amount of the gascan be controlled, and as heat taken away from the gas sensor element isreduced, it is possible to reduce the power consumption of the heaterfor heating the gas sensor element.

As described above, according to the present invention, it is possibleto provide the gas sensor with the high response speed, low powerconsumption, superior water splash resistance and a little settingdirection dependency and setting angle dependency.

Furthermore, in the gas sensor of the present invention, it ispreferable that the gas passage holes to be provided in the outer coverand the inner cover satisfy the following requirements:

First, it is preferable that the gas passage holes to be provided on theside surfaces of the outer cover and the inner cover are each of thesame shape. It is possible to equalize the inflow amount of the measuredgas in each gas passage hole by making gas passage holes uniform, sothat the dependency on the setting angle can be reduced.

Furthermore, it is preferable that two or more and eight or less gaspassage holes are provided. In this way, the gas flows in equally fromeach hole, and the setting directionality can be reduced. Only one gaspassage hole might cause the direction dependency, and if nine or moregas passage holes are provided, manufacturing costs of the covers mightbe increased.

Still further, it is preferable that the gas passage holes are providedat equal intervals in a circumferential direction of the cover. This canreduce the setting direction dependency.

Further yet, it is preferable that the above gas passage holes arearranged evenly at the same height in the axial direction. By arrangingthe gas passage holes evenly at the same height in the axial direction,it is possible to reduce the setting angle dependency and the settingdirection dependency.

Further yet, in the gas sensor of the present invention, the gas sensorelement can be applied to one that use a cup-shaped element (see FIG.14) besides a laminated element, as shown in FIG. 1. However, byapplying the present invention to the laminated element that is morefragile, the present invention functions more effectively.

Next, as one aspect of the present invention, it is preferable that thepartitions are constituted in a way to project from the inner surface ofthe outer cover to the inner cover in the sectional diameter directionof the gas sensor. This makes it possible to prevent the measured gasthat has got in from the gas passage hole on the outer cover frompassing other gas passage holes to flow out of the outer cover again,and further possible to rectify the gas flow between the outer cover andthe inner cover so that the measured gas can quickly reach the gaspassage hole of the inner cover along the partitions. In this way, sincethe measured gas can quickly reach the measured gas room inside theinner cover, it is possible to make the response speed of the gas sensorfaster.

Next, as one aspect of the present invention, it is preferable that thepartitions are constituted in a way to project from the outer surface ofthe inner cover to the outer cover in the sectional diameter directionof the gas sensor. This integrates the partitions with the inner cover,thereby lowering the setting cost of the partitions.

Furthermore, the gas flow can be rectified between the outer cover andthe inner cover so that the measured gas that has got in from the gaspassage hole on the outer cover may be prevented from passing other gaspassage holes to flow out of the outer cover again, and that themeasured gas can quickly reach the gas passage hole of the inner coveralong the partitions. In this case, since the measured gas can quicklyreach the measured gas room inside the inner cover, it is possible tomake the response speed of the gas sensor faster.

Next, as one aspect of the present invention, it is preferable that theprojection height of the partitions is ⅓ or more of a clearance betweenthe inner surface of the outer cover and the outer surface of the innercover. This makes it possible to enlarge a component in an axialdirection of the gas flow between the inner cover and the outer cover.

Furthermore, when the projection height is below ⅓ of the clearance, thecomponent in the axial direction of the gas flow is not very large,which might result in insufficient rectification effects to retain thesetting direction dependency and setting angle dependency.

The projection height is the distance between the inner surface of theouter cover and the inner surface of the partition. The clearance is thedistance between the outer surface of the inner cover and the innersurface of the outer cover. Examples of these are indicated as a, b inthe drawings of each Embodiment.

Next, as one aspect of the present invention, it is preferable that theaxial length of the partitions is ½ or more of the axial length of thegas passage hole. This makes it possible to enlarge the component in theaxial direction of the gas flow between the inner cover and the outercover.

If the axial length is shorter than ½, the measured gas might pass othergas passage holes to flow out of the outer cover again.

An upper limit of the axial length will be described later.

Next, as one aspect of the present invention, it is preferable that eachof the partitions is provided between two adjacent gas passage holesmade on the outer cover such that the partitions are circumferentiallyarranged. In this way, the gas flow can further be rectified between theouter cover and the inner cover, thereby making it possible to obtainmore of the effects in accordance with the present invention.

Next, as one aspect of the present invention, it is preferable that thepartitions are provided in the circumferential gaps communicating withthe plurality of gas passage holes made on the outer cover, and that theaxial length of the partitions is ½ or more of the axial length of thegas passage hole. This makes it possible to further rectify the gas flowbetween the outer cover and the inner cover, thereby allowing not onlyto obtain more of the effects in accordance with the present inventionbut also to enlarge the component in the axial direction of the gas flowbetween the inner cover and the outer cover. If the axial length isshorter than ½, the measured gas might pass other gas passage holes toflow out of the outer cover again.

Next, as one aspect of the present invention, it is preferable that thepartitions are constituted of concave parts made toward the inside in asectional diameter direction on the side surface of the outer cover.

Furthermore, as one aspect of the present invention, it is preferablethat the partitions are projections provided in the circumferential gapscommunicating with the plurality of gas passage holes made on the sidesurface of the outer cover, and that these projections provide cuts onpart of the side surface of the outer cover, and the partitions areconstituted by bending the cut part. In this case, the partitions can bemade integrally with the outer cover by applying punching-bendingforming to the outer cover, thereby making it possible to reduceprocessing work and material costs.

Next, as one aspect of the present invention, it is preferable that anend portion of the partitions on the base end side in an axial directionof the gas sensor does not reach the gas passage hole provided on theinner cover. In this case, however relative positions of the inner coverand the outer cover in a diametric direction, which are rectangular tothe axial direction of the gas sensor, may be determined, the flow ofthe measured gas is not obstructed and the responsiveness is difficultto get worse.

That is, the responsiveness hardly changes between the case where theouter cover is set to the inner cover at a predetermined angle and thecase where the outer cover is set as a position at which the outer coveris rotated at an arbitrary angle from the predetermined angle above.Therefore, it is not necessary to determine the positional relations ofthe inner cover and the outer cover when both the covers are set,thereby making possible to lower setting cost.

If the end portion of the partitions on the base end side reaches thegas passage hole on the inner cover, in other words, since the endportion of the partitions on the base end side overlaps the gas passagehole on the inner cover, the responsiveness might get worse. In order toprevent this, it is necessary to contrive in such a way as to set theouter cover in a position not to obstruct the gas flow to the gaspassage hole of the inner cover, which might increase the setting cost.

Next, as one aspect of the present invention, it is preferable that thegas sensor element is board-shaped, and that its sectional shape in adiametric direction of the inner cover is elliptic or square. This makesit possible to reduce not only the capacity in the inner cover but alsothe capacity of the measured gas room formed inside the cover. Thus, theresponsiveness of the gas sensor can be enhanced.

Next, as one aspect of the present invention, it is preferable that theaxial distance along the axial direction of the gas sensor between thegas passage hole provided closest to the tip end side on the inner coverand the gas passage hole provided closest to the base end side on theouter cover is 5 mm or more. This can prevent the water drops that havegot in from the gas passage hole on the side surface of the outer coverfrom getting inside the cover from the gas passage hole of the innercover. At this time, the water drops are discharged from the gas passagehole on the outer cover different from the gas passage hole throughwhich the water drops has got into, or the water drops evaporate in thegap between the outer cover and the inner cover. If the axial distanceis below 5 mm, the water drops that have got in from the gas passagehole of the outer cover get inside the inner cover, which might lead tothe element crack caused by the water splash or the like.

Next, as one aspect of the present invention, it is preferable that theouter cover and the inner cover are in a shape having a bottom, and thedistance between bottom surfaces of both covers are in a range of 0 to 5mm. This can prevent the measured gas that has got in from the gaspassage hole on the outer cover from directly getting out from anopening of the bottom surface, thereby allowing the response speed to befaster.

If the distance between the bottom surfaces exceeds 5 mm, the gas thathas got in from the gas passage hole on the outer cover might directlyget out from the opening of the bottom surface. The distance between thebottom surfaces is the distance between the inner surface of the outercover and the outer surface of the inner cover.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view in section of essential parts in an axialdirection in the vicinity of measured gas side covers of a gas sensor,in an embodiment 1 (sectional view cut along the line B-B of FIG. 2).

FIG. 2 is a plan view showing a bottom surface of the measured gas sidecovers in the embodiment 1.

FIG. 3 is an explanatory view in section of the gas sensor in adiametric direction in the embodiment 1 (sectional view cut along theline A-A of FIG. 1).

FIG. 4 is an explanatory view in section of the gas sensor in theembodiment 1.

FIG. 5 is a diagram showing the relation among the presence of apartition, a setting angle and a 63% response time.

FIG. 6 is a diagram showing the relation between the projection heightof the partition and the 63% response time.

FIG. 7 is an explanatory view in section of essential parts in an axialdirection in the vicinity of the measured gas side covers in which asection of the inner cover is elliptic, in the embodiment 1.

FIG. 8 is an explanatory view in section of essential parts in adiametric direction in the vicinity of the measured gas side covers inwhich the section of the inner cover is elliptic, in the embodiment 1(sectional view cut along the line C-C of FIG. 7).

FIG. 9 is an explanatory view in section of essential parts in an axialdirection in the vicinity of the measured gas side covers having thepartitions constituted by bending an outer cover, in an embodiment 2.

FIG. 10 is an explanatory view in section of the gas sensor in adiametric direction in the embodiment 2 (sectional view cut along theline D-D of FIG. 9).

FIG. 11 is an explanatory view in section of essential parts in an axialdirection in the vicinity of the measured gas side covers whosepartitions are V-shaped, in an embodiment 3 (sectional view cut alongthe line F-F of FIG. 12).

FIG. 12 is a plan view showing the bottom surface of the measured gasside covers in the embodiment 3.

FIG. 13 is an explanatory view in section of the gas sensor in adiametric direction, in the embodiment 3 (sectional view cut along theline E-E of FIG. 11).

FIG. 14 is an explanatory view in section of essential parts in an axialdirection in the vicinity of the measured gas side covers whose gassensor element is cup-shaped, in an embodiment 4.

FIG. 15 is a plan view showing the bottom surface of the measured gasside covers in the embodiment 4.

FIG. 16 is an explanatory view in section of essential parts in an axialdirection in the vicinity of the measured gas side covers whose fourpartitions are V-shaped, in an embodiment 5 (sectional view cut alongthe line I-I of FIG. 17).

FIG. 17 is a plan view showing the bottom surface of the measured gasside covers in the embodiment 5.

FIG. 18 is an explanatory view in section of the gas sensor in adiametric direction in the embodiment 5 (sectional view cut along theline H-H of FIG. 16).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

An embodiment of a gas sensor in accordance with the present inventionwill be described with FIG. 1 to FIG. 8. As shown in FIG. 1 to FIG. 4,the gas sensor comprises a gas sensor element 19 and a cylindricalhousing 10 for inserting and fixing the gas sensor element 19, measuredgas side covers 2 having a bottom and provided on a tip end side of thehousing 10 and an atmosphere side cover 31 provided on a base end side,and an upper cover 32. The measured gas side covers 2 comprise an innercover 22 for directly covering the gas sensor 19 and an outer cover 21directly exposed to measured gas ambience.

A measured gas room 20 is provided inside the inner cover 22, and onside surfaces of the inner cover 22 and the outer cover 21, gas passageholes 210 and 220 are each provided which are for leading a measured gasinto the measured gas room 20.

The gas passage hole 210 provided on the outer cover 21 is disposed in aposition much closer to the tip end side (lower part of the drawings inFIG. 1 and FIG. 4 is the tip end side) than the gas passage hole 220provided closest to the tip end side in the inner cover 22. Between theouter cover 21 and the inner cover 22, partitions 25 disposed extendedlyin an axial direction of the gas sensor are provided.

Hereafter, it will be described in detail. A gas sensor 1 in accordancewith present embodiment is set in an exhaust system of an automobileengine, and used for combustion control of the engine. An exhaust gas isled in as the measured gas, and as shown in FIG. 1, the gas sensorelement 19 constituted to detect oxygen density in the exhaust gas isbuilt in. A reference numeral 190 in accordance with FIG. 1 indicates agas detector unit.

As shown in FIG. 4, the measured gas side covers 2 constituted doubly ofthe outer cover 21 and the inner cover 22 are connected to the tip endside of the cylindrical housing 10, and the atmosphere side cover 31 isconnected to the base end 20 side of the housing 10. On a body of thehousing 10, a screw part 101 is provided which is screwed into a screwhole disposed in the exhaust system in which the gas sensor 1 is placed.Further, a flange part 102 that contacts the exhaust system is provided.

The gas sensor element 19 is inserted and disposed in the housing 10.Between the gas sensor element 19 and an inner surface of the housing10, an electrical porcelain 121, a powder 122, a packing 123 and aninsulator 124 are filled. In addition, the measured gas room 20, whichwill be indicated below, and the atmosphere side ambience in theatmosphere side cover 31 and the upper cover 32 that are on the base endside of the gas sensor 1, are airtightly separated by the powder 122 orthe like. The atmosphere side cover 31 is directly connected to thehousing 10. The upper cover 32 is connected to the base end side of theatmosphere side cover 31. An electrical porcelain 35 is provided insidethe upper cover 32.

Furthermore, an outer cover 33 is provided on the base end side of theupper cover 32 via a water-repellent filter 34. Atmosphere leading holes330 and 320 are disposed in a position where the upper cover 32 and theouter cover 33 confront the water-repellent filter 34, through which theatmosphere is led into the atmosphere side ambience formed inside theupper cover 32 and the atmosphere side cover 31. Further, a rubber bush136 is provided inside the base end side of the upper cover 32.

Furthermore, in order to take out outputs from the gas sensor element19, or to electrify a heater (not shown) built in the gas sensor element19, lead wires 133 and 134 are extendedly provided on the outside of thegas sensor 1 via connectors 131 and 132. Four connectors and four leadwires are given to the gas sensor 1 in the present embodiment. However,because parts of them are in positions where they can not be seen in thedrawing, they are omitted from the description.

Next, the measured gas side covers 2 will be described as shown in FIG.1 to FIG. 4.

The measured gas side covers 2 in the present embodiment have a doubleconstitution comprising the outer cover 21 and the inner cover 22. Bothof the covers 21 and 22 are cylindrical and have bottoms, and theirsectional shape is circular. Both of them are provided with the gaspassage holes 210 and 220 on the side surfaces, and gas passage holes219 and 229 are provided also in the centers of bottom surfaces 218 and228. The bottom surface 228 of the inner cover 22 and the bottom surface218 of the outer cover 21 are joined by spot welding. The gas passageholes 219 and 229 on the bottom surfaces 218 and 228 of each cover 21and 22 are overlapped. Further, the section of the gas sensor element 19is rectangular, and an axial center of the gas sensor element 19 and theaxial center of measured gas side covers 2 are disposed in a way tocorrespond to each other, and the corresponded axial center is G (seeFIG. 3).

As shown in FIG. 1 and FIG. 3, the gas passage hole 210 provided on theside surface is disposed in a position such that the distance betweenthe center of the gas passage hole 210 and the bottom surface 218 alonethe axial center of the gas sensor element 19 is 4 mm. This distance mayvary depending on the distance between the end portion position on thetip end side of the gas passage hole 210 and the bottom surface 218.Further, the gas passage hole 210 is circular and has a diameter of 2mm, and six gas passage holes 210 are arranged in line at equalintervals in a circumferential direction.

As shown in FIG. 2, the gas passage hole 219 provided on the bottomsurface 218 is a circular hole having a diameter of 2 mm in the centerof the bottom surface 218, and one gas passage hole 219 is provided.

As shown in FIG. 3, between each of six gas passage holes 31 provided onthe side surface, six partitions 25 are provided which project towardthe inner cover 22.

The shape of the partitions 25 is rectangular and has a size of 2 mm inthe circumferential direction and 4 mm in the axial direction, and theirprojection height a is 0.8 mm. A clearance b between the inner cover 22and the outer cover 21 is 1 mm. The projection height a is the distancebetween an inner surface 216 of the outer cover 21 and an inner surface256 of the partition 25 (symbol O indicates an extension line thatextends the inner surface 216 up to the position of the partition 25).

The partitions 25 in the present embodiment are formed by applying pressforming to corresponding parts of the outer cover 21 and producingconcave parts that project to the side of the inner cover 22 in thediametric direction. In addition, the clearance b is the distancebetween an outer surface 225 of the inner cover 22 and the inner surface216 of the outer cover 21. As shown in FIG. 1, an axial length c of thepartitions 25 is 4 mm, and an axial length d of the gas passage hole 210is 2 mm.

The axial length c of the partitions 25 is measured by the distance ofthe side facing the inner cover 22. The same applies to the axial lengthd of the gas passage hole 210. Further, the gas passage hole 220provided on the side surface of the inner cover 22 is disposed in aposition at a height of 15 mm from the bottom surface 228. This is basedon the distance between the end portion position on the tip end side ofthe gas passage hole 220 and the bottom surface 228.

In the gas sensor element 19, spots that function as the gas detectorunit 190 are within a range of about 6 to 10 mm from the bottom surface228, and the gas passage hole 220 is positioned closer to the base endside than the gas detector unit 190.

The gas flow of the exhaust gas that is the measured gas in the gassensor 1 in the present embodiment will be described. The flow of themeasured gas that gets in from the gas passage hole 210 provided on theside surface of the outer cover 21 is restricted by the partitions 25,so that the exhaust gas scarcely flows out directly to the outside fromthe gas passage holes 210 other than the gas passage hole 210 from whichthe exhaust gas has flown in.

The measured gas that has flown in from one gas 25 passage hole 210flows to the base end side in an axial direction, and then gets into themeasured gas room 20 formed inside the inner cover 22 from the gaspassage hole 220 provided on the side surface of the inner cover 22.Since the bottom surfaces 218 and 228 of both the covers 21 and 22 arehermetically stuck and have no distance, the measured gas scarcely flowstoward the tip end side.

Next, performance of the gas sensor 1 in the present embodiment will bedescribed. The gas sensor having the partitions in accordance with thepresent embodiment and the gas sensor that is of the same type as theformer one but does not have the partitions are each set in a pipe ofthe actual automobile engine, and the setting angle at this time ischanged every 15 in a range of −30 to +30. The setting angle is theangle formed by a normal direction of the pipe that constitutes theexhaust system and the axial direction of the gas sensor.

The engine is started in this state, and the 63% response time when thecombustion state of the engine is switched from rich to lean ismeasured. The measurement results are indicated in FIG. 5. According toFIG. 5, the farther the setting angle is away from 0, the worse theresponsiveness becomes. However, it is evident that in any state the gassensor with the partitions has the shorter response time and superiorresponse.

Furthermore, several gas sensors different in the projection heights ofthe partitions are prepared, and the 63% response time is measured foreach of them in the same way as above. The measurement results of theseare indicated in FIG. 6. A projection height of 0 mm indicates the stateof no partitions, and a projection height of 1 mm indicates the state inwhich the partitions 25 hermetically stick to an outer surface 226 ofthe inner cover 22. When the partitions 25 have a height of 1 mm, theclearance is 0 between both the covers 21 and 22 in the part where thepartitions 25 are provided, so that both the covers 21 and 22 arepartitioned by the partitions 25.

According to FIG. 6, it is evident that the response time is short andthe responsiveness is low when the projection height of the partitionsis low, and that the higher the projection height becomes, the betterthe responsiveness becomes. Further, it is evident that when theprojection height becomes ⅓ or more of the clearance, the responsivenessis especially enhanced.

Next, the functional effects of the gas sensor in the present embodimentwill be described. The gas sensor in the present embodiment is providedwith the partitions 25 disposed extendedly in the axial directionbetween the outer cover 21 and the inner cover 22. Consequently, themeasured gas that has got in from the gas passage hole 210 on the outercover 21 can be prevented from passing other gas passage holes 210 toflow out of the outer cover 21 again, and moreover, the gas flow can berectified between the outer cover 21 and the inner cover 22 so that themeasured gas can quickly reach the gas passage hole 220 on the innercover 22 along the partitions 25. In this way, the measured gas canreach the measured gas room 20 inside the inner cover 22, therebyenabling the response speed of the gas sensor 1 to be faster.

Furthermore, since the partitions 25 function as guide plates of themeasured gas, the measured gas can be led into the measured gas room 20from the gas passage holes 210 and 220 always in the same state, withoutdepending upon the setting direction and the setting angle of the gassensor 1. As a result, it is possible to obtain gas responsiveness thatis not dependent upon the setting direction and the setting angle.

Still further, the gas passage hole 210 provided on the outer cover 21is disposed in a position closer to the tip end side than the gaspassage hole 220 provided closest to the tip end side in the inner cover22. This makes it possible to prevent the gas passage holes 210 and 220on both the covers 21 and 22 from being in a confronting state, and toprevent water drops from getting in from the outside. In this way, thegas sensor in accordance with the present embodiment has high watersplash resistance.

In particular, in the case where the water drops collected in the pipeof the exhaust system right after the start of the engine splash ontothe measured gas side covers 2 of the gas sensor 1, the water drops donot reach the gas detector unit 190 if the gas passage hole 210 on theouter cover 21 and the gas passage hole 220 on the inner cover 22 arekept away in the axial direction, thereby making it possible to preventthe crack of the gas sensor element 19 caused by the water splash.Further, as it is not necessary to enlarge the diameter of the gaspassage hole to enhance the responsiveness, the inflow amount of the gascan be restricted, and as heat taken away from the gas sensor element isreduced, it is possible to reduce the power consumption of the heaterfor heating the gas sensor element.

As described above, according to the present embodiment, it is possibleto provide the gas sensor with the high response speed, low powerconsumption, superior water splash resistance and a little settingdirection dependency and setting angle dependency. Further, as shown inFIG. 7 and FIG. 8, when the sectional shape of the inner cover 22 iselliptic, it is also possible to have the same effects as in the presentembodiment. In addition, the gas sensor of this shape in particular canreduce the capacity of the measured gas room formed inside the coversince its sectional shape made elliptic, thereby making it possible tohave the gas sensor with higher responsiveness.

Embodiment 2

As shown in FIG. 9 and FIG. 10, in the gas sensor in accordance with thepresent embodiment, the partitions 25 are constituted by making cuts onpart of the side surface of the outer cover 21 and bending the cut part.Further, the partitions 25 are provided between one gas passage hole 210and another adjacent gas passage hole. The projection height a of thepartitions 25 is 0.8 mm, and the clearance b is 1 mm. The others are thesame as in Embodiment 1, and the functional effects are also the same.

Embodiment 3

As shown in FIG. 11 to FIG. 13, in the gas sensor in the presentembodiment, the outer cover 21 is hollowed on its side surface to beV-shaped when seen in terms of the sectional shape in the diametricdirection, from the top end (vicinity of the bottom surface) of theouter cover 21 to a position to surpass a portion m of the gas passagehole 210 on the outer cover 21 and not to reach a portion n of the gaspassage hole 220 on the inner cover 22, whereby the partitions 25 areformed. Further, the partitions 25 are disposed in all parts between theadjacent gas passage holes 210 on the outer cover 21. The projectionheight a of the partitions 25 is 0.8 mm, and the clearance b is 1 mm.The others are the same as in Embodiment 1, and the functional effectsare also the same.

Embodiment 4

As shown in FIG. 14 and FIG. 15, the gas sensor in accordance with thepresent embodiment comprises a cup-shaped gas sensor element 195 madefrom a solid electrolyte that is cylindrical and has a bottom. Themeasured gas side covers 2 comprising the outer cover 21 and the innercover 22, and the partitions 25 are of the same shape as those inEmbodiment 3. The axial center of the cup-shaped gas sensor element 195and the axial center of the measured gas side covers 2 are disposed tocorrespond to each other. The others are the same as in Embodiment 1,and the functional effects are also the same.

Embodiment 5

As shown in FIG. 16 to FIG. 18, in the gas sensor in accordance with thepresent embodiment, four gas passage holes 210 are provided on the outercover 21 along the diametric direction, and the partitions 25 aredisposed in all parts between the adjacent gas passage holes 210. Thatis, the number of the partitions 25 is also four. The projection heighta of the partitions 25 is 0.8 mm, and the clearance b is 1 mm. Theothers are the same as in Embodiment 1, and the functional effects arealso the same.

1. A gas sensor comprising a gas sensor element and a cylindricalhousing for inserting and fixing said gas sensor element, measured gasside covers having a bottom and provided on a top end side of saidhousing and an atmosphere side cover provided on a base end side,wherein said measured gas side covers comprise an inner cover fordirectly covering the gas sensor element and an outer cover directlyexposed to measured gas ambience, and are provided with a measured gasroom inside said inner cover, gas passage holes for leading a measuredgas into said measured gas room are provided on side surfaces of saidinner cover and said outer cover respectively, and the gas passage holeprovided on said outer cover is disposed in a position much closer to atop end side than the gas passage hole provided closest to the top endside in said inner cover; and partitions disposed to extend in an axialdirection of the gas sensor are provided between said outer cover andsaid inner cover, each of said partitions being formed by a concavityprovided on the side surface of said outer cover in such a manner thatsaid concavity is projecting radially inwardly, each of said partitionshaving an axial length which is equal to or greater than an axial lengthof said gas passage hole provided on said side surface of said outercover, wherein each said partition is disposed between two adjacent gaspassage holes of said outer cover.
 2. A gas sensor comprising a gassensor element and a cylindrical housing for inserting and fixing saidgas sensor element, measured gas side covers having a bottom andprovided on a top end side of said housing and an atmosphere side coverprovided on a base end side, wherein said measured gas side coverscomprise an inner cover for directly covering the gas sensor element andan outer cover directly exposed to measured gas ambience, and areprovided with a measured gas room inside said inner cover, gas passageholes for leading a measured gas into said measured gas room areprovided on side surfaces of said inner cover and said outer coverrespectively, and the gas passage hole provided on said outer cover isdisposed in a position much closer to a top end side than the gaspassage hole provided closest to the top end side in said inner cover;and partitions disposed to extend in an axial direction of the gassensor are provided between said outer cover and said inner cover, eachof said partitions being formed by a concavity provided on the sidesurface of said outer cover in such a manner that said concavity isprojecting radially inwardly, each of said partitions having an axiallength which is equal to or greater than an axial length of said gaspassage hole provided on said side surface of said outer cover, whereinsaid partitions are disposed so as to be circumferentially spaced fromsaid gas passage holes of said outer cover.
 3. A gas sensor comprising agas sensor element and a cylindrical housing for inserting and fixingsaid gas sensor element, measured gas side covers having a bottom andprovided on a top end side of said housing and an atmosphere side coverprovided on a base end side, wherein said measured gas side coverscomprise an inner cover for directly covering the gas sensor element andan outer cover directly exposed to measured gas ambience, and areprovided with a measured gas room inside said inner cover, gas passageholes for leading a measured gas into said measured gas room areprovided on side surfaces of said inner cover and said outer coverrespectively, and the gas passage hole provided on said outer cover isdisposed in a position much closer to a top end side than the gaspassage hole provided closest to the top end side in said inner cover;and partitions disposed to extend in an axial direction of the gassensor are provided between said outer cover and said inner cover, eachof said partitions being formed by a concavity provided on the sidesurface of said outer cover in such a manner that said concavity isprojecting radially inwardly, each of said partitions having an axiallength which is equal to or greater than an axial length of said gaspassage hole provided on said side surface of said outer cover, whereinsaid concavities project radially inwardly substantially to the sidesurface of said inner cover.
 4. A gas sensor comprising a gas sensorelement and a cylindrical housing for inserting and fixing said gassensor element, measured gas side covers having a bottom and provided ona top end side of said housing and an atmosphere side cover provided ona base end side, wherein said measured gas side covers comprise an innercover for directly covering the gas sensor element and an outer coverdirectly exposed to measured gas ambience, and are provided with ameasured gas room inside said inner cover, gas passage holes for leadinga measured gas into said measured gas room are provided on side surfacesof said inner cover and said outer cover respectively, and the gaspassage hole provided on said outer cover is disposed in a position muchcloser to a top end side than the gas passage hole provided closest tothe top end side in said inner cover; and partitions disposed to extendin an axial direction of the gas sensor are provided between said outercover and said inner cover, each of said partitions being formed by aconcavity provided on the side surface of said outer cover in such amanner that said concavity is projecting radially inwardly each of saidpartitions having an axial length which is equal to or greater than anaxial length of said gas passage hole provided on said side surface ofsaid outer cover, wherein there are a plurality of gas passage holesdefined circumferentially of said outer cover and a correspondingplurality of partitions provided to project toward the inner coverbetween respectively adjacent gas passage holes.
 5. The gas sensoraccording to claim 4, wherein there are six gas passage holes definedcircumferentially of said outer cover and six partitions provided toproject toward the inner cover between respectively adjacent gas passageholes.